The photoreactions of the carboxylate complexes of 5,10,15,20-tetra(2-N-methylpyridyl) porphyrin

Anaerobic aqueous solutions of a selection of alkyl and substituted alkylcarboxylic acids, in the presence of iron(III) 5,10,15,20-tetra(2-N-methylpyridyl)porphyrin have been irradiated with light (lambda >390 nm). In all the reactions this brought about the photolysis of an iron(III) porphyrin-carboxylate complex (monitored by UV-vis spectroscopy) to give the iron(II) porphyrin and carboxyl radical. The fate of the carboxyl radical following decarboxylation, has been investigated by EPR spectroscopy using spin-traps. These studies show that substituents have a marked influence on the rate and course of the reactions. In the presence of dioxygen the system is catalytic since the iron(II) porphyrin is rapidly oxidised to the iron(III) species. Supporting the catalyst on silica gel greatly improves the stability of the catalyst to self oxidation (bleaching).